Certain proteins, referred to as growth factors, sustain neural cells in the brain. Examination of the expression of such factors with age and disease may reveal factors associated with cell death, as well as define new therapeutic approaches for Alzheimer's disease. Polypeptides such as neuronal growth factors of myelin-associated neuronal regeneration inhibitory factors may be involved in neuronal survival in degenerative diseases. Initial studies have focused on regulation of the neurotrophin class of nerve growth factor (NGF-like) and their receptors (the trk family of proto-oncogenes) in Alzheimer's disease, while future studies will be directed towards investigation of newly characterized polypeptides that are associated with inhibition of neuronal regeneration in the CNS.